The invention relates to a process and apparatus for extracting ingredient substances from natural products by means of a pressure fluid, particularly for decaffeinating tea leaves by means of carbon dioxide, wherein the ingredient substances are bound by an adsorbent, preferably activated carbon.
It is known to introduce, e.g., tea leaves in a high-pressure vessel through which pressurized carbon dioxide is conducted in axial direction. The effluent carbon dioxide is fed to a separate adsorber for binding the caffeine. Furthermore, it is known to recycle the carbon dioxide for this purpose.
The known procedure involves considerable disadvantages. Thus, very slender and long vessels have to be used for stability reasons which results in enormous dumping heights. This, in turn, leads to extended extraction times because the carbon dioxide flow velocity has to be low. In such an arrangement, the first tea leaf layers in flow direction remain exposed to the carbon dioxide flow even when the caffeine has already been extracted. However, the process must be continued until the last tea leaf layers in flow direction have been treated. By the time this has happened, the carbon dioxide has also extracted the aroma from all the preceding layers.
Another disadvantage is that tea leaf layers tend to agglomerate when flow velocities are high. Moreover, the type of construction causes part of the ingredient substances dissolved in the gas to precipitate on the vessel wall as well as in pipes and valves and results in clogging. A further disadvantage is that, at a constant carbon dioxide flow velocity through the tea leaf layers, the decaffeination rate gradually decreases with increasing caffeine load in the carbon dioxide.
It is the primary object of the present invention to improve the process described above by reducing the time required for the treatment of the natural product. Another object of the invention is to shorten the flow path of the loaded fluid thereby diminishing the risk of clogging and, in particular, to reduce the fluid flow velocity.